Most commonly used automotive vehicles include ventilation and temperature control systems. These systems commonly provide circulation for the air in the vehicle's passenger compartment to make the air less stuffy. They commonly enable a selectable amount of air from the outside to be blown into the passenger compartment to provide cool or fresh air. They usually include a heater to enable the air in the passenger compartment to be heated. In addition, in many automotive vehicles they include air conditioning which enables the air in the passenger compartment to be cooled and dried.
In many automotive ventilation systems a grill runs along the vehicle's cowling parallel to, and just in front of, the base of the windshield. When the vehicle moves, air pressure tends to build up in front of the windshield, causing air to be blown into this grill. This air is channeled into the vehicle's ventilation system which is commonly located under its dashboard. Commonly an electric fan is provided to increase the flow of air. This is particularly useful when the vehicle is moving too slowly for air to be blown into the ventilation system with much force.
The ventilation system normally contains a heat core, which is a radiator through which part of the cooling fluid which exits the vehicle's internal combustion engine passes once it has passed through the engine and absorbed waste heat from it. The heated cooling fluid which passes through the heat core transfers a portion of its heat to the air of the ventilation system which passes through the heat core.
Normally the ventilation system includes doors, or air valves, which control the flow of air in it. Traditionally some such air valves (often in the form of passenger adjustable louvers) help control how much air flows through each of the ventilation system's various vents into the passenger compartment. Other air valves control what percent of the air entering the passenger compartment passes through the heat core, controlling the extent to which that air is heated.
Heat core heaters are efficient because they use what would otherwise be the wasted thermal energy generated by their vehicle's internal combustion engine to heat the passenger compartment. Unfortunately, it often takes several minutes after the internal combustion engine has been turned on before the engine's coolant fluid is hot enough to provide large amounts of heat to the passenger compartments. In cold weather this delay in the provision of heat to the passenger compartment can be uncomfortable and unpleasant.
In many automotive vehicles the ventilation system also includes air conditioning. Traditional automotive air conditioning systems use a refrigerant fluid which evaporates at a relatively low temperature. They include an evaporator in which the refrigerant is evaporated at low pressure to remove heat from air to be cooled. They have a compressor to convert the low pressure evaporated refrigerant gas from the evaporator into a hotter, higher pressure gas. A condenser, which looks something like a radiator, cools the hot, high pressure refrigerant gas from the compressor and condenses it into a high pressure liquid. This high pressure liquid is stored in a fluid reservoir, and a portion of it is released through a pressure reduction valve into the evaporator, so that the liquid refrigerant which enters the evaporator is of a sufficiently low pressure that it will evaporate at the temperature of the air to be cooled.
Such traditional automotive air conditioning systems work quite well, but they have the drawback that it usually takes some time before they can provide a sufficient volume of cool air into the passenger compartment to properly cool that compartment. This is a particular problem in hot climates or on hot day in any climate. It can be a particular problem when a parked car has been left in the sun on a hot day and its interior has reached a high temperature.